Monthly Archives: September 2010

Just the facts, ma’am

The 1950s television drama Dragnet is famous for Detective Joe Friday’s laconic line, “Just the facts, ma’am” — even though these were not quite his words.* The president of the American Academy of Forensic Sciences has a similar request. In the “President’s Message” in the September Academy News, Joseph P. Bono described testimony in which “I eliminated from my arguments the following: philosophy, psychology, probability theory, statistics, differential equations and all those other ‘things’ frequently used to attack forensic science. What a novel idea! I focused on facts.”

Now I have have nothing against facts. I collect them myself. But without a little philosophy, I would not know what they are, and I have yet to see a differential equation used to attack forensic science. What then, is Mr. Bono complaining about? Is it the academic criticism of pattern and impression evidence analysts who testify that they can link a single individual or object to a latent fingerprint, tool mark, and so on, with a probability of 1 — criticism that draws on elementary ideas in philosophy, psychology, and probability and statistics? Is the target the recommendation of a Congressionally mandated National Research Council committee on strengthening forensic science that serious and scientifically defensible efforts be made to quantify the rates of error in the methods that these analysts use? Are these the “things” he believes forensic scientists or criminalists should avoid?

Mr. Bono importunes “those who represent both sides in the courtroom [to] pay more attention to the forensic science report and testimony, and the reliability for both.” Id. at 4. But surely the “facts” that bear on the “reliability” (that is, the accuracy) of a forensic science report and testimony include the extent to which the technique yields a false result under conditions comparable to the ones in the case at bar, just as they include the steps that the witness took to avoid arriving at a false result.

With DNA evidence, there was debate over whether proficiency tests should be used to estimate a error probability in a specific case. Some scientists argued in favor of doing so, while others insisted that the proficiency test data would not provide a useful estimate of the chance of an error in a given case. But no one thought it possible to avoid addressing the accuracy of DNA testing for identity by advising witnesses to use Joe Friday’s line, “All we know are the facts, ma’am.” Probabilities and statistics are facts too.

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* According to Michael J. Hayde, My Name’s Friday (2001), the actual statement was “All we want are the facts, ma’am,” or “All we know are the facts, ma’am.”  Id. at 72-7.